The most important step of a titration analysis is the determination of the final stage or end-point of the titration. It is the state in which the amounts of the substance to be analyzed and of the titrating agent are balanced. Among various known methods of indication of the titration end-point, there are visual, photometric, electrochemical and others. The accuracy, correctness and the available concentration limits depend on the sensitivity of such methods. One of the most sensitive electrochemical methods is the amperometric indication based on one or two indication electrodes. These methods permit titrations up to concentrations of 10.sup.-5 to 10.sup.-6 mol/l and in certain very specific cases up to 10.sup.-7 mol/l. See e.g. Cooke, Reilley, Furman, "Sensitive End-Point Procedure for Coulometric Titrations," 23 Anal. Chem. 1662 (November 1951), and, Myers, Osteryoung, "Amperometric Titrations Employing Differential Pulse Polarography," 46 Anal. Chem. 356, (March 1974). Concentrations of up to 5.times.10.sup.-8 mol/l are also known in connection with coulometric titrimetry. See: Champion, Marinenko, Taylor, "Determination of Submicrogram Amounts of Chromium by Coulometric Titrimetry," 42 Anal. Chem. 1210, (September 1970).
The limiting factors in known apparatuses for amperometric indication of the end-point of titration are the low current signals produced at low-level concentrations of the substances to be analyzed, the unfavorable signal to noise ratio and some disturbing background currents from which particularly the capacitive charging current limits the concentration limit and the sensitivity of the titration.